The present invention is directed to thermally stable polycrystalline diamond (TSP) materials and to the engineered TSP materials having desired properties that may vary through the material thickness and/or width and to such materials forming the cutting layers of tools such as the cutting layers of cutting elements used in earth boring bits.
A conventional cutting element 1, such as a shear cutter mounted on an earth boring bit typically has a cylindrical cemented carbide body 10, i.e. a substrate, having an end face 12 (also referred to herein as an “interface surface”), as for example shown in FIG. 1. An ultra hard material layer 18, such as polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) is bonded on the interface surface forming a cutting layer. The cutting layer can have a flat or curved interface surface 14. Cutting elements are mounted on pockets 2 of an earth boring bit, such a drag bit 7, at an angle 8, as shown in FIGS. 1 and 2 and contact the earth formation 11 during drilling along edge 9 over cutting layer 18.
Generally speaking, the process for making a cutting element employs a substrate of cemented tungsten carbide where the tungsten carbide particles (also referred to as “grains”) are cemented together with cobalt. The carbide body, i.e., substrate, is placed adjacent to a layer of ultra hard material particles (grains) such as for example diamond or cubic boron nitride (CBN) within a refractory metal enclosure, typical referred to as a “can”, as for example a niobium can, and the combination is subjected to a high temperature at a high pressure where diamond or CBN is thermodynamically stable. This process is referred to as a high pressure high temperature sintering process. This results in the re-crystallization and formation of a polycrystalline diamond or polycrystalline CBN ultra hard material layer on the cemented tungsten carbide substrate, i.e., it results in the formation of a cutting element having a cemented tungsten carbide substrate and an ultra hard material cutting layer. The ultra hard material layer, if made from polycrystalline diamond (PCD), may include tungsten carbide particles and/or small amounts of cobalt. Cobalt promotes the formation of PCD. Cobalt may also infiltrate the diamond from the cemented tungsten carbide substrate.
The cemented tungsten carbide substrate is typically formed by placing tungsten carbide powder (i.e., grains) and a binder in a mold and then heating the binder to its melting temperature causing the binder to melt and infiltrate the tungsten carbide grains fusing them together and cementing the substrate. Alternatively, the tungsten carbide powder may be cemented by the binder during the high temperature, high pressure process used to re-crystallize the ultra hard material layer. In such case, the substrate material powder along with the binder are placed in the can, forming an assembly. Ultra hard material grains are provided over the substrate material to form the ultra hard material polycrystalline layer. The entire assembly is then subjected to a high temperature, high pressure process forming the cutting element having a substrate in a polycrystalline ultra hard material layer over it.
With many of the aforementioned cutting elements, the cutting layer is not efficient for all types of earth formation drillings. Similarly, with other types of cutting tools, the cutting layers of such cutting tools are not efficient for the various types of cutting that they are used. As such, a cutting element or cutting tool having a cutting layer which is engineered for a specific cutting task is desired.